1. Field of the Invention
The present invention relates to a disk drive device, in particular, to a disk drive device improved in the stiffness of a fluid dynamic bearing while suppressing an increase in the size and deterioration in the drive performance of the fluid dynamic bearing.
2. Description of the Related Art
Hard disk drives (HDDs) are media used in storage devices of computers, etc. Devices that drive such recording disks are collectively termed disk drive devices. A disk drive device rotates, at high speed, a recording disk on which recording tracks for recording magnetic data are formed by a brushless motor. A magnetic head, which executes read/write of magnetic data from/in a recording disk, is arranged, with a slight gap, above the recording surface of the recording disk so that the recording tracks are traced.
In many cases, fluid dynamic bearings are used in the bearing units of such disk drive devices. The general structure of a fluid dynamic bearing is disclosed in, for example, Japanese Patent Application Publication No. 2000-304052. The fluid dynamic bearing is provided with dynamic pressure grooves in part of a rotating body, such as a shaft, so that dynamic pressure is generated by interaction with the lubricant, such as oil, which is filled around the rotating body, when the rotating body is rotating. The bearing supports a load by making the rotating body in the lubricant maintain in a non-contact state by spacing the rotating body apart from surrounding components with the use of the generated dynamic pressure.
The rotational accuracy of a disk drive device has been drastically improved by providing such a fluid dynamic bearing, thereby allowing for a larger volume of magnetic data to be stored in a higher density. As a result, disk drive devices, which are provided with fluid dynamic bearings, have been mounted in various apparatuses and used in extensive environments. For example, the disk drive devices have more often been mounted in mobile devices. Under such situations of use, it has been requested that a disk drive device attains a stable rotational drive and is capable of normally executing the reading/writing of magnetic data, even if an impact and so forth is applied to the disk drive device or apparatus in which the disk drive devices is mounted. In particular, for disk drive devices that are mounted in mobile devices, there is a tendency that impact resistance is considered to be important.
The present inventors have recognized that, in a disk drive device, it is desirable that a thrust position of the recording disk is designed not to vary in order to stably maintain the operations of the disk drive device even if an impact is applied thereto in the thrust direction. That is, the inventors have recognized that it is effective to enhance the stiffness in the thrust direction of a fluid dynamic bearing. For example, a disk drive device is taken into consideration, in which the disk drive device comprises: a flange that is fixed to a shaft for rotating a recording disk; and a sleeve that includes a flange housing portion that rotatably houses the flange and that houses the shaft. In this case, because the flange has a function of generating dynamic pressure in the thrust direction, the stiffness in the thrust direction can be improved when the diameter of the flange is increased. However, in a disk drive device that is strongly needed to be small in size, it is undesirable that the housing, which forms the shape of the disk drive device, is made larger. Therefore, making the diameter of the flange larger induces the arrangement space of the drive unit to be compressed, the drive unit being arranged on the outer circumference side of the flange. If the drive unit becomes small, the drive current for generating required torque is increased, thereby causing the required performance of the electronic device, in which the disk drive device is mounted, sometimes not to be fulfilled. Alternatively, when the drive current is not increased, the maximum torque is decreased and the rotation becomes unstable accordingly, thereby sometimes deteriorating the accuracy of the reading/writing of magnetic data.